1. Field of the Invention
The invention relates to a method for the position and/or speed control of a linear drive. The linear drive can, in particular, be a servo drive for a linear robot. The method provides that an electric motor is supplied via a converter having a control unit. The motor position is determined, in particular, in a sensor-free manner or via a position sensor. Furthermore, the invention also relates to a circuit layout for carrying out the method.
2. Discussion of Background Information
A known servo drive comprises an electric motor that is mechanically coupled to a position-measuring system. A servo converter with its output stage supplies the motor with, energy via a cable. The information of the position sensor is guided back to the servo amplifier with a cable. This is called position feedback. The measured position is differentiated to the speed. The rotational-speed controller is dependent on a high quality of the position signal, since a measurement noise or quantization noise appears amplified in the position signal due to the differentiation. The position controller directly processes the position signal and the position specification. A highly dynamic control of a servo drive therefore requires a position detection with high resolution, which conflicts with an economical solution because it is expensive.
With the highest demands on the control quality, the disadvantages of the differentiation can be eliminated by additionally using an acceleration sensor. The measured position and the acceleration are converted in a so-called observer into a speed signal with a considerably lower noise component, such as is indicated, e.g., in Hiller, B; Lehner W-D.: Verbesserung der Regelgüte durch Ferraris-Sensoren. Antriebstechnik 40, 2001, No. 4. The disadvantage of these solutions are the high additional costs for the acceleration sensor and the cabling.
Another device for obtaining a dynamically high-quality, partially synthesized signal for the acceleration of the rotor of a drive is known from DE 198 51 003 A1.
More economical solutions can be achieved, in theory, if a cost-effective sensor with a low resolution is used. Alternatively, the position measurement can be omitted completely if a sensor-free method for position determination is used, as is known, e.g., from EP 0 539 401 B. The disadvantage of both solutions is the low quality of the control, which is not acceptable in the application as linear robot.